然后我突然意识到他们是非法移民。用英语怎么说？

然后我突然意识到他们是非法移民。

Then I twigged that they were illegal immigrants...

then

adv. 那时，然后，那么，话说回来；adj. 当时的，那时的；

例句
Liz adjusted her mirror and then edged the car out of its parking bay.
莉兹调了调后视镜，将车子挪出了停车位。

twigged

adj. 有细枝的，有嫩枝的；

例句
Then I twigged that they were illegal immigrants...
然后我突然意识到他们是非法移民。

that

det. 那个，那；pron. 那个，那；conj. 多么，如此…以至，用于某些动词、形容词和名词后，引出各种从句；adv. 不那么，那样；

例句
...expensive make-up that we saw being advertised by a beautiful model...
我们所见的由一位漂亮模特代言的昂贵化妆品

they

pron. 他/她/它们，人们，大家，政府，当局，她们；

例句
The storms had abated by the time they rounded Cape Horn.
他们绕过合恩角时，暴风雨已经减弱。

were

be的过去时复数和第二人称单数形式，有时代替 was,用于条件从句、动词 wish 之后等；

例句
Shops, houses, and vehicles were set ablaze.
店铺、房子和车辆全都陷于火海。

illegal

adj. 不合法的，违法的，违反规则的；n. 非法移民，非法劳工，间谍；

例句
It's illegal to get into a formal agreement with investors that they'll buy in the aftermarket.
与投资者达成正式协议、允许他们在后市上买入的做法是非法的。

immigrants

n. 移民( immigrant的名词复数 )；

例句
Large numbers of immigrants flooded into the area...
大量移民涌入这个地区。